Method for stabilizing refractive index profiles using polymer mixtures

ABSTRACT

A method for making an optical element comprises polymerizing a first monomer to form a first polymer, the first polymer having a spatially varying degree of cure that provides a predetermined refractive index profile; and polymerizing a second monomer in the presence of the first polymer to form a second polymer intermixed with the first polymer, the second polymer stabilizing the first polymer and the refractive index profile.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to optical elements, such as correctivelenses, and to methods for making them. More particularly, thisinvention relates to optical elements containing two or more polymers.

2. Description of the Related Art

Many optical systems such as the human eye contain aberrations. Inattempting to correct for such aberrations, it is common to assume thatthe light passing through the system is limited to paraxial rays,specifically, rays that are near the optical axis and that are containedwithin small angles. Corrective optics produced according to thisassumption generally have only spherical surfaces. For example, it istypically assumed that ocular imperfections in the human eye are limitedto lower order imperfections, including the imperfections commonlycalled “astigmatism” and “defocus”, that can be corrected by lenseshaving spherical surfaces. However, higher order imperfections canexist, including but not limited to imperfections known as “coma” and“trefoil.” These imperfections unfortunately cannot be corrected byconventional glasses or contact lenses, leaving patients with less thanoptimum vision even after the best available corrective lenses have beenprescribed.

Moreover, it is often difficult to simultaneously minimize allaberrations. Indeed, corrections to an optical system to minimize onetype of aberration may result in the increase in one of the otheraberrations. For example, decreasing coma can result in increasingspherical aberrations. Furthermore, it is often necessary to correctaberrations in an optical system that are introduced duringmanufacturing. This process can be iterative and time consuming,requiring, as it does, assembly, alignment, and performance evaluationto identify aberrations, followed by disassembly, polishing or grindingto correct the aberrations, and then reassembling and retest. Severaliterations might be needed before a suitable system is developed.

U.S. patent application Ser. No. 09/875,447, filed Jun. 4, 2001,entitled “Wavefront Aberrator and Method of Manufacturing,” discloses,inter alia, a method for making a wavefront aberrator by using aphotopolymerization method to change the refractive index of a polymer.A refractive index profile may be formed by selectively curing thepolymer on a region-by-region basis by exposure to radiation (e.g., UVlight). The refractive index of the exposed polymer in the selectedregions increases, but the resulting refractive index profile is notpermanent, and over time, the refractive index profile changes and theamplitude of the induced refractive index change tends to decrease overtime.

SUMMARY OF THE INVENTION

A preferred embodiment provides an optical element comprising a firstoptical cover, a second optical cover, and a layer of polymeric materialsandwiched between the first optical cover and the second optical cover,wherein the polymeric material comprises a mixture of a first polymerand a second polymer, the first polymer having a spatially varyingdegree of cure that provides a predetermined refractive index profile,and the second polymer being cured to thereby stabilize the refractiveindex profile.

Another preferred embodiment provides a method for making an opticalelement, comprising:

polymerizing a first monomer to form a first polymer, the first polymerhaving a spatially varying degree of cure that provides a predeterminedrefractive index profile; and

polymerizing a second monomer in the presence of the first polymer toform a second polymer intermixed with the first polymer, the secondpolymer stabilizing the refractive index profile.

Another preferred embodiment provides a method for making an ophthalmiclens, comprising:

forming a mixture comprising a first monomer, a second monomer, a firstphotoinitiator, and a second photoinitiator;

placing the mixture between a first optical cover and a second opticalcover;

exposing the mixture to a first radiation source, thereby polymerizingthe first monomer to form a first polymer, the first polymer having aspatially varying degree of cure that provides a predeterminedrefractive index profile; and

exposing the second monomer to a second radiation source, therebypolymerizing the second monomer to form a second polymer intermixed withthe first polymer

These and other embodiments are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be readily apparent fromthe following description and from the appended drawings (not to scale),which are meant to illustrate and not to limit the invention, andwherein:

FIGS. 1A and 1B are cross-sectional views schematically illustrating apreferred optical element. FIG. 1C is a cross-section view schematicallyillustrating selective polymerization to form a polymer having aspatially varying degree of cure that provides a predeterminedrefractive index profile. FIG. 1D is a plot schematically illustratingthe refractive index profile resulting from the selective polymerizationillustrated in FIG. 1C.

FIG. 2 is a flow chart illustrating a preferred method for making anoptical element.

FIG. 3 is a schematic diagram illustrating aberrations in a wavefront.

FIG. 4 is a schematic diagram illustrating an index of refractionprofile for a preferred lens that compensates for the aberrations shownin FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a preferred optical element 10. In FIG. 1A, theoptical element 10 includes a first rigid or flexible optical cover 12which may be a transparent plate, a second rigid or flexible opticalcover 14 which may be a transparent plate, and a layer of polymericmaterial 16 sandwiched between the first and second optical covers 12,14. If desired, a barrier 18 may be used to contain the polymericmaterial 16 between the first and second plates 12, 14 prior to, andfollowing, the curing described below. If desired, one or both of thefirst and second covers 12, 14 may comprise a curved surface which mayexhibit a pre-existing refractive power. Thus, the first and secondcovers 12, 14 may each individually be ophthalmic lenses, e.g., a singlevision lens, bifocal lens, or progressive addition lens, all of whichmay or may not include prism power. Alternatively, both of the first andsecond plates 12, 14 may be planar lenses having curved surfaces andwithout refractive power.

The polymeric material 16 is preferably made by polymerizing at leasttwo curable constituents such as two monomers 20, 22 with respectivepolymerization initiators as illustrated in FIG. 1B. The refractiveindex of each of the two monomers 20, 22 changes during polymerization(“curing”) to form the polymeric material 16. Curing is preferablyconducted by exposing the two monomers 20, 22 to a radiation source,such that the degree of curing varies between locations within thepolymeric material 16, as described in greater detail below. The indexof refraction profile is determined by the degree of curing orpolymerization of the two monomers. The first monomer 20 is preferablypolymerized to form a first polymer having a spatially varying degree ofcure that provides a predetermined refractive index profile, and thesecond monomer 22 is preferably uniformly polymerized or cured to form asecond polymer, thereby stabilizing the first polymer and the refractiveindex profile. The polymeric material 16 thus comprises a mixture of thefirst polymer and the second polymer. Those skilled in the art willunderstand that the term “polymeric material” as used herein is a broadterm that encompasses various monomers and polymers, as well asmonomer/monomer, monomer/polymer, and polymer/polymer mixtures.

In the illustrated embodiment, the two monomers 20, 22 each cure byexposure to different wavelengths of light. By way of non-limitingexample, the first monomer 20 can cure by exposure to relatively longultraviolet wavelength light (e.g., “UVA”) and the second monomer 22 cancure by exposure to relatively short ultraviolet wavelength light (e.g.,“UVB”). The first monomer 20 can be, e.g., an acrylate or vinyl ether,and the second monomer 22 can be, e.g., a vinyl ether or an epoxy.Combinations of first and second monomers can include acrylates andepoxies, thiol-enes and esters, thiol-enes and epoxies, acrylates andvinyl ethers, and vinyl ethers and epoxies.

Other monomers that polymerize by photoinitiation may also be used.Suitable monomers include, for example, urethanes, thiol-enes, celluloseesters, mercapto-esters, and epoxies. The first monomer and/or thesecond monomer can be a monomer system that contains two or moremonomers that react with one another. For example, thiol-ene is apreferred first monomer that comprises thiol monomers and ene monomers.A wide variety of thiol-ene monomers and polymers are known to thoseskilled in the art, see, e.g., Jacobine, A. T. in “Radiation Curing inPolymer Science and Technology: Photopolymerization Mechanisms,” Eds. J.P. Fouassier and J. F. Rabek, Elsevier Applied Science: London, pp.219-268 (1993). Preferably, the first and/or second monomers arephotopolymers. The monomer may polymerize spontaneously uponirradiation, or, preferably, a photoinitiator may be used. Suitablephotoinitiators include alpha cleavage photoinitiators such as thebenzoin ethers, benzil ketals, acetophenones, and phosphine oxides;hydrogen abstraction photoinitiators such as the benzophenones,thioxanthones, camphorquinones and bisimidazole; and cationicphotoinitiators such as aryldiazonium salts, arylsulfonium andaryliodonium salts, and ferrocenium salts. Alternatively, otherphotoinitiators such as the phenylphosphonium benzophene salts, aryltert-butyl peresters, titanocene, or N-methylmaleimide may be used.

In a preferred embodiment, the polymerization process is controlled bythe duration and intensity of the UV light exposure. More preferably,the polymerization should be substantially stopped when the UV lightsource is turned off. Thiol-ene polymerization systems, for example,exhibit this “step growth” characteristic. FIG. 2 is a flow chartillustrating a preferred method for making the optical element 10. Atblock 24 a light source selectively polymerizes the first monomer 20 tocreate a polymeric material 16 having a spatially varying degree of curethat provides a refractive index profile that approximates therefractive index profile desired for the resulting optical element 10.FIG. 1C schematically illustrates how such selective polymerization maybe carried out. By subjecting areas in which a greater degree ofpolymerization is desired to higher levels of irradiation (indicated bymultiple arrows 30 in FIG. 1C), and subjecting areas in which a lowerdegree of polymerization is desired to lower and intermediate levels ofirradiation (indicated by a single arrow 35 and a double arrow 38,respectively), a polymer having a spatially varying degree of cure maybe formed that provides a predetermined refractive index profile asillustrated in the plot shown in FIG. 1D. Suitable selectivepolymerization methods are disclosed in U.S. Patent ApplicationPublication No. 2002/0080464 A1 and 2003/0143391 A1, which are herebyincorporated by reference in their entireties and particularly for thepurpose of describing such methods. Since the monomer 20 has an index ofrefraction that changes upon polymerization, the refractive index in aparticular region can be controlled by controlling the degree ofpolymerization or cure in that region by selective irradiation. Monomer20 is preferably polymerized using a photoinitiator that responds to afirst wavelength of light. The second monomer 22 may be present duringthe polymerization of the first monomer 20 or may be diffused intopolymeric material 16 after polymerization of the first monomer 20. Ifpresent during the polymerization of the first monomer 20, secondmonomer 22 preferably undergoes little or no polymerization during thepolymerization of the first monomer 20.

At block 26, the exposure to the first wavelength of light isterminated, ceasing the curing of the first monomer 20, thereby ceasingthe change of the index of refraction. The refractive index profile ofthe optical element 10 at this stage approximates the desired refractiveindex profile. For example, as shown in FIG. 1C, the amount of firstpolymer 40 in the region of optical element 10 exposed to lower amountsof radiation 35 is less than in the regions exposed to greater amountsof radiation 30, 38. The spatially varying refractive index profileillustrated in the plot shown in FIG. 1D reflects the respective amountsof first polymer 40 in each region. Thus, by spatially varying thedegree of cure of the first polymer 40, the refractive index profile atvarious points 42, 44, 46 generally corresponds with the intensity ofincident radiation 35, 30, 38 (respectively). Then, at block 28 a lightsource is activated to irradiate the material 16 with a secondwavelength of light that, preferably, substantially completely anduniformly cures the second monomer 22. An excess of light may be used inblock 28 to ensure complete polymerization. However, less than 100%curing of the second monomer can also be effective to stabilize theindex profile. For example, when the polymeric material 16 has aviscosity value of greater than about 20,000 centipoise prior topolymerization of the second monomer 22, a degree of cure of about 40%for the second monomer may be sufficient. In general, the higher theviscosity of the polymeric material 16, the lower the degree of curingof the second monomer 22 required to stabilize the refractive indexprofile. Preferably, the amount of the second monomer is about 15% ormore by weight in relation to the first monomer, so that when the secondpolymer component is substantially completely cured, it forms a lockingnetwork throughout the entire polymer mixture and renders the firstmonomer/polymer component substantially immobile.

A preferred embodiment for making the polymer mixture 16 involves theuse of a relatively low molecular weight first monomer that containsrelatively few (preferably three or four) polymerizable functionalgroups per monomer molecule. For example, a preferred first monomermixture may comprise thiol-ene, more preferably a thiol-ene comprising athiol that contains three or four-SH groupss per molecule, and an enethat contains three or four carbon-carbon double bonds per molecule.Those skilled in the art are aware of additional examples, see Jacobine,A. T., in “Radiation Curing in Polymer Science and Technology:Photopolymerization Mechanisms,” Eds. J. P. Fouassier and J. F. Rabek,Elsevier Applied Science: London, pp. 219-268 (1993). By usingrelatively low molecular weight first monomers, the magnitude of therefractive index change due to volume shrinkage or densification ismaximized. Thus, monomers are preferably chosen to increase the dynamicrange of the index of refraction change, or the delta-N value.

The second monomer (which may be a mixture of monomers) may comprise amacromer, e.g., a relatively low or intermediate molecular weightpolymer that contains reactive groups such as an unsaturated bisphenol-Afumarate polyester (e.g., ATLAC, available commercially from Reichhold,Inc. Research Triangular Park, NC). A preferred ATLAC containsapproximately 40 ene groups and is soluble in acetone and in variousthiol-ene mixtures. Preferably, the second monomer has a relatively highviscosity, as compared to the first monomer, to thereby slow thediffusion of the low molecular weight components of the first polymer.For example, in a preferred thiol-ene/ATLAC combination, use of therelatively high viscosity ATLAC as the second monomer preferably slowsthe diffusion of portions of the thiol-ene monomer/polymer mixture(prepared by prior polymerization of the first thiol-ene monomer) thatare uncured or cured to a relatively low degree. Similar macromerscontaining reactive functional groups can be used as a component of thesecond monomer. Subsequent polymerization of the second monomerpreferably forms a very high viscosity matrix that stabilizes the firstpolymer (and thereby stabilizing the refractive index profile) byslowing or preventing diffusion of the components of the first polymer,and particularly the lower molecular weight components of the firstpolymer (such as first monomer and oligomers thereof). Preferably, thedegree of curing of the second monomer to form the second polymer issubstantially uniform in a spatial sense, such that the degree of cureof the second polymer does not undesirably affect the intendedrefractive index profile.

The second polymer may also stabilize the first polymer by the formationof covalent bonding between them. For example, in preferredthiol-ene/ATLAC systems, upon photo-polymerization, the low molecularweight thiol and ene monomers polymerize to form a denser and morecompact polymer, resulting in an increase in the index of refraction.The low molecular weight thiol and/or ene monomers, and/or the growingthiol-ene polymer, also preferably react with the ATLAC. The higherindex regions formed by the thiol-ene polymerization are thus stabilizedby the covalent bonding of such units to the ATLAC. Without the ATLAC,the low molecular weight thiol-ene units are relatively free to migrateby diffusion; hence the desired higher index of refraction regions tendto diffuse away over time, resulting in the stability problems discussedabove.

Another method of stabilizing the refractive index profile formed by thespatially varying degree of cure is to use an entirely different type ofpolymer as the second component to stabilize the index profile. Forexample, one may first use a photo-polymerization process as describedabove to generate the desired index of refraction profile, then insteadof using a second monomer that is cured by UV light to form a secondpolymer that provides increased stability, one can use a second monomerthat is cured by heating as illustrated in block 28 in FIG. 2. One suchexample is an epoxy which is thermally curable, e.g., instead of ATLACin the embodiment discussed above, a thermally curable epoxy is usedinstead. The steps used to form the desired index of refraction profileremain essentially the same, then heat is applied to cure the epoxy,thereby stabilizing the first polymer in an epoxy matrix.

One embodiment is to choose an epoxy that cures at relatively low (e.g.,below 80° C.) or close to room temperature. The thiol, ene, and epoxy isthen kept near or below room temperature to prevent the curing of theepoxy. The index profile may then be created by activating thephoto-initiator that induces the thiol-ene polymerization. When thedesired index of refraction profile is reached, the system is warmed upslightly to reach the epoxy curing temperature, polymerizing the epoxyturns and freezing-in the thiol-ene polymer to thereby stabilize theindex of refraction profile.

Another embodiment is a method of stabilizing the index of refractionprofile by curing thermally. Once the index of refraction profile iswritten in the polymer mixture, it is preferable to avoid degrading theindex profile. Heating the epoxy could potentially degrade the profile.One method of minimizing that risk is to perform the epoxy curing in twosteps: First, the second polymer in the mixture is allowed to gel(partially polymerize) at room temperature after the writing of theindex profile in the polymer, and then the temperature is raised, e.g.,to about 60° C. to 85° C., to complete the full curing process. The gelstate provides a high viscosity environment around the index profile andthereby decreases the diffusion rate of the first polymer, e.g., thephoto-polymerized thiol-ene polymer. The complete curing at elevatedtemperature stabilizes the index profile.

The patent application entitled “Apparatus and Method for Curing ofUV-Protected UV-Curable Monomer and Polymer Mixtures,” Ser. No.10/848,942, filed May 18, 2004, and the application to which it claimspriority, U.S. Provisional Application No. 60/472,669, filed on May 21,2003, are hereby incorporated by reference in their entireties, andparticularly for the purpose of describing preferred methods for makingthe polymeric material 16.

Reference is made to FIG. 3 to illustrate how the desired refractiveindex profile can be determined. Those skilled in the art willunderstand from the discussion above that the first monomer 20 (whichmay be a mixture of monomers) is partially cured in a manner that variesspatially to achieve the desired refractive index profile, and that thecuring of the second monomer 22 (which may also be a mixture ofmonomers) may change the refractivity somewhat. Preferably, an overallprofile is obtained that is the combination of the desired refractivityindex distribution resulting from selective polymerization of the firstmonomer 20 and the added change in refractivity over the entire material16 that results from the curing of the second monomer 22.

A schematic illustration of a wavefront 30 is shown in FIG. 3, showing adivergent wave which may consist of spherical, astigmatism and highorder aberrations. The higher order aberrations are typicallydescribable by third and higher order terms of Zernicke polynomials. Atan imaginary cross sectional plane 32, the wavefront has intersectionslocated at points 34, 36, 38, 40. The peak of the wavefront is indicatedat 42, which is traveling ahead of the intersections 34, 36, 38, 40. Thedistance between the peak 42 and the intersections is typicallyexpressed in the units of physical distance in space. The peak 42 has aprojected point 44 on the plane 32.

To correct the aberrations in this wavefront, a refractive index profileis created in the material 16 that will slow down the peak 42.Accordingly, the desired refractive index profile for a portion of thematerial 16 is one that exhibits, after curing, an index of refractionthat results in the conjugate of the wavefront 30 such that a plane waveexits the optical element 10. An illustrative curing profile is shown inFIG. 4, which has a three dimensional distribution profile 46 that isessentially identical to that of the profile of the wave 30 shown inFIG. 3.

Specifically, in one preferred, non-limiting embodiment, the retardationrequired for compensation can be calculated as follows. The differenceof the index of refraction, Δn between cured and uncured material 16 istypically in the range of 0.001 to 0.05 and may be determined by routineexperimentation. The retardation is the physical distance “d” betweenthe wave peak 42, and its projection point 44 on the plane 32. Thethickness of the material 16 consequently is at least d/Δn. In thecuring profile for the material 16, the scale of the magnitude of theretardation is such that the magnitude of thickness of the curedmaterial or the integrated index difference at a profile peak 46 to itsprojection 48 on a cross-sectional plane 50 is d/Δn. The effect of sucha refractive index profile is that the peak 42 of the wave 30 willexperience the most retardation, and the wave at the intersections 34,36, 38, 40 experiences no retardation at corresponding locations 52, 54,56, 58 of the refractive index profile in the uncured portion of thematerial 16. Accordingly, the desired refractive index profile of thematerial 16 after curing is such that its index of refractionestablishes a profile that matches the profile of the wave for whichcompensation is desired.

The curing can be undertaken using a light source in combination with abeam shaping unit. Preferably, the light source with beam shaping unitcreates a light beam that is substantially collimated. It should beappreciated, however, that a non-collimated beam may also be used ifdesired. In one exemplary, non-limiting embodiment, the light beam maypass through a focusing lens to form a converging, or focusing, lightbeam that is directed toward the optical element 10, where the lightbeam passes through the first transparent plate 12 to focus on a desiredvolume in the material 16. This irradiates the monomer at that location,preferably activating the photoinitiator and beginning the curingprocess within the material 16. The curing process results in acorresponding change of the index of refraction within the material.Terminating the exposure to the light ceases the curing, thereby ceasingthe change of the index of refraction.

The activation and power level of the light source and its position arepreferably controlled by a controller which is electrically connected tothe light source and to shuttling components on which the source may bemounted. In a preferred embodiment, the converging light beam passesthrough the transparent plate 12 and converges within the material 16.Specifically, the light ray edges of the beam converge at the desiredfocal point to cure the material 16 at the focal point. Then, the lightbeam is moved to another point adjacent to the just-cured point to curethe next point, and so on. The details of various methods of lightenergy delivery by beam scanning have been disclosed in U.S. PatentApplication Publication No. 2003/0143391 A1, which is herebyincorporated by reference in its entirety and particularly for thepurpose of describing such methods.

While the term “focal point” is used herein, it is to be understood thatthe light beam at its point of focus is not at a true “point”, which inmathematics has no volume, but rather is focused in a volume referred toas a “beam waist” which represents the region in the material 16undergoing by exposure to the converging light beam. Generally speakingand without limitation, a beam with a cone angle that is in the range of0.002 radians to 1.5 radians may be used.

Preferably, the distance between curing volumes should be less than thebeam waist of the light beam, creating an overlap region. In a preferredembodiment, the size of the beam overlap region can vary in the range ofabout ten to about seventy five percent (10%-75%) of the size of thebeam waist. In a particularly preferred, non-limiting embodiment, thesize of the beam overlap region can vary in the range of about forty toabout sixty percent (40%-60%) of the size of the beam waist. In oneembodiment in which a tightly focused beam is preferred, the beam waistis in the range of twenty microns (20 μm) or less. However, beam waistsin the range of about 0.1 micron to about two hundred microns may beused. It is to be understood that the curing volumes can be sequentialand contiguous to each other, or the scan sequence may be randomlyaccessed, such that the new curing location can be isolated from theprevious location, with no overlap of the beam waists.

Other methods for selectively curing the monomers (e.g., a photomask)may also be used. Suitable selective polymerization methods aredisclosed in U.S. Patent Application Publication No. 2002/0080464 A1,which is hereby incorporated by reference in its entirety andparticularly for the purpose of describing such methods.

Preferred optical elements may be used to correct aberrations in opticalcomponents such as telescopes, microscopes, ophthalmic diagnosticinstruments including confocal scanning ophthalmoscopes, and funduscameras. In such cases, the viewing instrument generally includesrefractive elements such lenses, reflective elements such as mirrors andbeam splitters, and diffractive elements such as gratings and acousto-and electro-optical crystals. Preferred embodiments may be used toeliminate costly manufacturing of such apparatus by using less costlyoptics and by compensating for the attendant residual aberrations withcorrecting elements such as are described above. In a preferredembodiment, the optical element 10 shown in FIG. 1 is a correctingelement configured as, for example, an ophthalmic lens, to correctaberrations caused by imperfections in a patient's eye.

It will be appreciated by those skilled in the art that variousomissions, additions and modifications may be made to the processesdescribed above without departing from the scope of the invention, andall such modifications and changes are intended to fall within the scopeof the invention, as defined by the appended claims.

1. An optical element comprising: a first optical cover, a secondoptical cover, and a layer of polymeric material sandwiched between thefirst optical cover and the second optical cover; wherein the polymericmaterial comprises a mixture of a first polymer and a second polymer,the first polymer having a spatially varying degree of cure thatprovides a predetermined refractive index profile, and the secondpolymer being cured to thereby stabilize the refractive index profile.2. The optical element of claim 1, in which the first and second opticalcovers are transparent plates.
 3. The optical element of claim 1 inwhich the first and the second optical covers are ophthalmic lenses. 4.The optical element of claim 2 in which the first polymer and the secondpolymer form a pair selected from the group consisting ofpolyacrylate/epoxy, polyacrylate/polyvinyl ether, thiol-enepolymer/polyester, thiol-ene polymer/epoxy, and polyvinyl ether/epoxy.5. The optical element of claim 1 in which the first polymer is selectedfrom the group consisting of thiol-ene polymer, epoxy, polyacrylate andpolyvinyl ether.
 6. The optical element of claim 1 in which the secondpolymer is selected from the group consisting of epoxy, polyester,polyacrylate and polyvinyl ether.
 7. A method for making an opticalelement, comprising: polymerizing a first monomer to form a firstpolymer, the first polymer having a spatially varying degree of curethat provides a predetermined refractive index profile; and polymerizinga second monomer in the presence of the first polymer to form a secondpolymer intermixed with the first polymer, the second polymerstabilizing the refractive index profile.
 8. The method of claim 7 inwhich the second monomer and first polymer are sandwiched between firstand second cover plates during the polymerizing of the second monomer.9. The method of claim 8 in which the first and second cover plates areophthalmic lenses.
 10. The method of claim 7 in which the polymerizingof the first monomer is conducted by exposing the first monomer to afirst radiation source.
 11. The method of claim 10 in which the firstmonomer comprises a photoinitiator.
 12. The method of claim 10 in whichthe polymerizing of the second monomer is conducted by exposing thesecond monomer to a second radiation source different from the firstradiation source.
 13. The method of claim 7 in which the first monomeris selected from the group consisting of epoxy, thiol, ene, acrylate,vinyl ether, and mixtures thereof.
 14. The method of claim 7 in whichthe second monomer is selected from the group consisting of epoxy,acrylate, ester and vinyl ether.
 15. The method of claim 7 comprisingintermixing the first monomer and the second monomer prior to thepolymerizing of the first monomer.
 16. The method of claim 7 in whichthe first polymer is a thiol-ene polymer and the second polymer isselected from the group consisting of epoxy polymer and unsaturatedpolyester.
 17. A method for making an ophthalmic lens, comprising:forming a mixture comprising a first monomer, a second monomer, a firstphotoinitiator, and a second photoinitiator; placing the mixture betweena first optical cover and a second optical cover; exposing the mixtureto a first radiation source, thereby polymerizing the first monomer toform a first polymer, the first polymer having a spatially varyingdegree of cure that provides a predetermined refractive index profile;and exposing the second monomer to a second radiation source, therebypolymerizing the second monomer to form a second polymer intermixed withthe first polymer.
 18. The method of claim 17 in which substantially allof the second monomer is consumed by the polymerizing of the secondmonomer.
 19. The method of claim 17 in which the second polymer ispartially cured.
 20. The method of claim 17 in which the first and thesecond optical covers are selected from the group consisting oftransparent plate, plano ophthalmic lens, single vision ophthalmic lens,bifocal ophthalmic lens, and progressive addition ophthalmic lens.